1. Field of the Invention
This invention relates to a radio controlling device, and more particularly to a motor servo circuit used in the radio controlling device which is designed to improve control precision and to decrease power consumption.
2. Description of the Prior Art
A motor servo circit has been extensively used heretofore to control amount of movement in various objects to be controlled. For example, in a radio controlling device which remotely controls running objects, such as, for example, model air planes, model boats, or model cars, by an electromagnetic wave, a rotating angle and direction of servo motor in the motor servo circuit are controlled by the electromagnetic waves which are emitted from a transmitter and received by a receiver mounted on the objects to be controlled. The motor servo circuit in the radio controlling device is generally constructed as shown in FIG. 1.
The motor servo circuit includes an input terminal t.sub.1 which receives a pulse S having a pulse width as shown in FIG. 2(a) corresponding to a controlled variable in an operating station after being received by the receiver (not shown) and subjected to shape its wave form. The pulse S is introduced into a pulse generator MM.sub.1 for triggering and obtaining a single pulse M as shown in FIG. 2(b).
The pulse width of the pulse M shown in FIG. 2(b) is controlled in response to a resistance of a variable resistor VR having a fixed terminal to which a power source +V is connected and a slider connected to a rotary shaft of motor which will be hereinafter described.
The input pulse S and the output pulse of the pulse generator MM.sub.1 are fed to an exclusive OR circuit consisting of inverters IN.sub.1, IN.sub.2, NOR circuits NR.sub.1, NR.sub.2 and an OR circuit OR. When the width of the pulse S is greater than that of the pulse M, a pulse e.sub.1 (hereinafter referred to as an error pulse) having width corresponding to the difference between the widths of two pulses S and M is generated at an output terminal of the NOR circuit NR.sub.1 as shown in FIG. 2(c).
When the width of the pulse M is greater than that of the pulse S, an error pulse e.sub.2 shown in FIG. 2(d) having width corresponding to the difference between the width of two pulses S and M is generated at an output terminal of the NOR circuit NR.sub.2.
The error pulses e.sub.1 and e.sub.2 are fed to a set terminal S and a reset terminal R of flip-flop FF.sub.1, respectively, to make either one of the output terminals Q or Q "1." At the same time, the error pulses e.sub.1 and e.sub.2 are fed to a pulse stretcher circuit PS through the OR circuit OR.sub.1 wherein they are stretched in a predetermined ratio as shown in FIG. 2(e). An output pulse from the pulse stretcher circuit PS is introduced into a motor driving circuit PA by passing through either one of AND circuits AD.sub.1 or AD.sub.2 so that a motor MT may be rotated in a predetermined direction, thereby to move controls (not shown) in a predetermined value.
As explained hereinabove, the slider of the variable resistor VR is connected to the rotary shaft of the motor MT. Thus, the resistance of the variable resistor VR is subjected to change in accordance with the rotation of the motor MT. If the changing direction of the resistance of the variable resistor VR is set to the direction where the pulse width of the output pulse M of the pulse generator MM.sub.1 is registered with that of the input pulse S, the resistance of the variable resistor VR is controlled extending over several cycles of the controlling waves which are received by the receiver. When the width of the input pulse S is registered with the width of the output pulse of the pulse generator MM.sub.1, the OR circuit OR.sub.1 stops generating the output which makes the revolution of the motor MT stop, thereby the control operation is achieved, for instance, by opening a throttle valve of an engine in response to the operation volume determined by the transmitting station.
In the radio controlling devices, a DC motor is mostly used as the motor MT. When the DC motor is energized by pulses, the average electric power supplied to the motor is increased by the application of the pulses having wider pulse width to the motor which results in the increase in the revolution speed. To the contrary, the revolution speed of the motor is decreased when the pulses having narrower pulse width are applied thereto, and the motor stops running when the pulse width of the applied pulses is narrower than a predetermined value. Under the condition, the motor does not rotate even if an electric current is running through the motor for driving, which makes it impossible to effect the controls in an appropriate position and consumes the electric power wastefully. When a battery is used as the power source, the battery is run out soon if the electric power is used in waste.
In order to prevent the battery from running out, the pulse stretcher circuit PS is usually constructed to include a transistor Q.sub.1 which is added to an integrated circuit consisting of a resistor R.sub.s and a capacitor C.sub.s, thereby to shape the wave forms by introducing an output of the capacitor C.sub.s into a Schmidt trigger circuit as shown in FIG. 3. When the error pulse e shown in FIG. 4(a) is fed to the base of the transistor Q.sub.1, the transistor Q.sub.1 is switched on so that the electric charge stored in the capacitor C.sub.s may be discharged as shown in FIG. 4(b), and then the capacitor C.sub.s is charged by current supplied through a resistor R.sub.s so as to be in equal to the power source +V. During the period of exceeding the terminal voltage of the capacitor C.sub.s at the time of discharging the capacitor C.sub.s beyond the discrimination level VH.sub.1 shown in FIG. 4(b) and exceeding the terminal voltage of the capacitor C.sub.s at the time of subsequent charging the capacitor C.sub.s beyond the discrimination level VH.sub.2 shown in FIG. 4(b), the Schmidt trigger circuit ST generates the pulse having the width corresponding to that of the error pulse e which is shaped as shown in FIG. 4(c) for driving the motor MT.
In this instance, the pulse width of the output pulse of the pulse stretcher circuit with respect to the error pulse e is determined by adjusting the value of time constant C.sub.s R.sub.s in a time constant circuit which consists of the capacitor C and the resistor R.sub.s. When the Schmidt circuit ST is used, which is capable of changing a positive feedback volume by adjusting a feedback resistor R.sub.f shown in FIG. 3, the minimum pulse width (hereinafter referred to as a minimum output pulse) fed to the motor MT through the driving circuit PA can be determined by adjusting the positive feedback volume so as to have such pulse width which does not cause a failure in starting the motor MT.
In recent years, the radio controlling devices have been diversified, and a variety of motors have been mounted on the objects which are subjected to the remote control.
In the motors used in the radio controlling devices, a starting voltage for motor is different in each type of the motors, and the motor having less number of poles is generally used to reduce the manufacturing cost of the running objects. The motor requiring a high starting voltage or having less number of poles does not start unless large average electric power is supplied therewith. Thus, it is necessary to set the pulse width of the minimum output pulse wider for driving such motor. In other words, the time constant determined by the capacitor C.sub.s and the resistor R.sub.s must be set to be larger. However, if the time constant is so large, the width of the output pulse of the pulse stretcher circuit P.sub.s is variable to a great extent in response to the change in the width of error pulse e as shown in FIG. 5, which results in the running of the motor MT at a full speed.
In FIG. 5, the pulse width of the error pulse e is shown in the abscissa, while the width of the output pulse of the pulse stretcher circuit P.sub.s is shown in the ordinate making the time constant C.sub.s R.sub.s a parameter. As shown in FIG. 5, the pulse width of the minimum output pulse will be broader and the inclination of its characteristics curve will be steeper in accordance with the increase in the time constant C.sub.s R.sub.s as shown in the broken lines (A), (B) and (C). As a result, the pulse width of the output pulse of the pulse stretcher circuit P.sub.s is easily saturated, thereby to make the motor MT rotate at the full speed.
In the radio controlling devices, the servo mechanism is required to have such characteristics that the motor can be quickly and precisely rotated in a predetermined position. Thus, even if the driving characteristics of the motor MT is improved by setting the time constant C.sub.s R.sub.s larger as explained hereinabove, the requirements for the servo mechanism are not satisfied unless the motor MT stops exactly at the required position.
On the other hand, it is possible to conduct delicate control and to increase resolving power of the servo mechanism, if the revolution speed of the motor is decreased by applying the minimum output pulse having the narrower pulse width to the motor MT. Therefore, it is advantageous that the time constant C.sub.s R.sub.s is as small as possible in terms of the increase in the resolving power.
As explained hereinabove, when determining the output pulse width of the pulse stretcher circuit P.sub.s, both requirements for the driving characteristics of the motor MT and the resolving power must be satisfied at the same time, however, as a matter of fact, this is impossible.
Even if the width of the minimum output pulse is determined by taking both the driving characteristics of the motor and the resolving power into consideration, it is required to conduct the troublesome adjustment every time when the motor is changed, because there is the variety in the characteristics of the motors as explained hereinabove. The adjusting operation is actually too complicated to do, which creates such problems that the sufficient control precision is not obtainable or the consumption of the electric power due to the current flowing into the motor which does not participate in driving the motor is increased.